THE prank worked better than its evil mastermind could have hoped for Sunday night at the Hard Rock Café in Phoenix. Express Scripts — one of the participants in a National Council of Prescription Drug programs confab at the nearby Hyatt Regency — was throwing a dance party. Express Scripts is being sued for $100 million in damages by Eliot Spitzer, who claims the firm inflated the cost of generic drugs, pocketed rebates intended for customers and sold patient information. Between songs, someone handed the lead singer of the Starlight Band a note. "I have an announcement. It's someone's birthday today, Eliot Spitzer," the clueless frontman said. "Where is Eliot?" The place went silent. Express Scripts executives started rushing to the stage and someone yelled, "He's in goddamn New York." But too late — the band had launched into a version of "Happy birthday, dear Eliot." One witness said, "It was the funniest thing I ever saw."